Testing the Survival of American Chestnut Seedlings

by Zoe Hoyle, SRS Science Communications • October 23, 2012

Stacy Clark in the field with American chestnut seedling. Photo by Rod Kindlund.

The American chestnut tree (Castanea dentata) dominated the forest canopy in the eastern United States for thousands of years, until it was decimated by an exotic fungal pathogen, the chestnut blight (Chryphonectria parasitica) in the early part of the 20th century. Since then, tree enthusiasts and scientists have been trying to find a way to produce an American chestnut tree with resistance to the blight. The American Chestnut Foundation (TACF), formed in 1983, has reached a point where they can test what is hypothesized to be a tree with blight-resistance that otherwise behaves like an American chestnut.

Efforts to test the reintroduction of blight-resistant chestnut seedlings have been underway since 2007, when TACF, the U.S. Forest Service, and The University of Tennessee(UT) began collaborating on chestnut restoration research on national forests lands. TACF provided material to the Forest Service for the establishment of eleven field plantings that included 4,596 trees, 2,022 of which were the first potentially blight-resistant seedlings raised through TACF back cross breeding efforts. Stacy Clark, research forester with the Southern Research Station Upland Hardwood Ecology and Management unit, leads these efforts for the Forest Service and recently shared findings from the first 3 years.

“At four of the field plantings, chestnuts have high survival (75 percent) rates and are growing a foot in height per year,” says Clark. “The tallest trees planted are staying above competition and deer browse, with some trees capable of growing over 16 feet in three years. It’s still too early to test for blight resistance, but after three growing seasons, we’ve determined that initial seedling quality at planting was important to establishment success.”

At seven planting sites, the researchers discovered new factors that are negatively affecting restoration success. “Survival is relatively low (59 percent) in these plantings due to root rot caused by an exotic fungus, Phytophthora cinnamomi,” says Clark. “The future of chestnut restoration in the southern United States, where this pathogen is present, will require growing seedlings for planting using soil and water free of the disease (e.g., containers), and planting on sites that do not have the disease (e.g., previously uncultivated land).”

Other exotic pests affecting seedlings included the Asiatic oak weevil (Cyrtepistomus castaneus), the Asian gall wasp (Dryocosmus kuriphilus), and Asian ambrosia beetles (Coleoptera: Scolytidae). These exotic pests will have negative impacts on chestnut restoration, and there are currently no adequate control methods for them. Native pests may also take their toll on restoration plantings. Researchers observed severe cicada damage on one planting, and the rarely observed chestnut sawfly (Craesus castaneae) was noticed defoliating experimental seedlings and natural sprouts.

“Successful reintroduction of the American chestnut will require far more than blight-resistance,” says Clark. “Perhaps the greatest challenge will be the ability of blight-resistant seedlings to survive and reproduce in a forest that contains both native and non-native threats.”